Speech coding technologies can compress speech signals to save transmission bandwidth and increase the capacity of a communication system. With the popularity of the Internet and the expansion of the communication field, the speech coding technologies are a focus of standardization in China and around the world. Speech coders are developing toward multi-rate and wideband, and the input signals of speech coders are diversified, including music and other signals. People require higher and higher quality of conversation, especially the quality of music signals. For different input signals, coders of different coding rates and even different core coding algorithms are applied to ensure the coding quality of different types of signals and save bandwidth to the utmost extent, which has become a megatrend of speech coders. Therefore, identifying the type of input signals accurately becomes a hot topic of research in the communication industry.
A decision tree is a method widely used for classifying signals. A long-term decision tree and a short-term decision tree are used together to decide the type of signals. First, a First-In First-Out (FIFO) memory of a specific time length is set for buffering short-term signal characteristic variables. The long-term signal characteristics are calculated according to the short-term signal characteristic variables of the same time length as the previous one, where the same time length as the previous one includes the current frame; and the speech signals and music signals are classified according to the calculated long-term signal characteristics. In the same time length before the signals begin, namely, before the FIFO memory is full, a decision is made according to the short-term signal characteristics. In both the short-term decision and the long-term decision, the decision trees shown in FIG. 1 and FIG. 2 are applied.
In the process of developing the present invention, the inventor finds that the signal classifying method based on a decision tree is complex, involving too much calculation of parameters and logical branches.